// Next returns the next term available from this reader.
// Returns error NoMoreTerms if the reader can't find any more terms.
func (r *TermReader) Next() (term.Term, error) {
var t term.Term
var ll *lex.List
if r.readTerm(1200, r.ll, &ll, &t) {
if term.IsError(t) {
return nil, fmt.Errorf("%s", t.String())
}
r.ll = ll
return term.RenameVariables(t), nil
}
return nil, NoMoreTerms
}
func (cp *headbodyCP) Follow() (Machine, error) {
// rename variables so recursive clauses work
clause := term.RenameVariables(cp.clause).(term.Callable)
// does the machine's current goal unify with our head?
head := clause
if clause.Arity() == 2 && clause.Name() == ":-" {
head = term.Head(clause)
}
env, err := cp.goal.Unify(cp.machine.Bindings(), head)
if err == term.CantUnify {
return nil, err
}
MaybePanic(err)
// yup, update the environment and top goal
if clause.Arity() == 2 && clause.Name() == ":-" {
return cp.machine.SetBindings(env).PushConj(term.Body(clause)), nil
}
return cp.machine.SetBindings(env), nil // don't need to push "true"
}